A column of drilling fluid, usually referred to as mud, is customarily provided in a borehole while drilling the borehole through subsurface formations. Usually, the weight of the mud is carefully selected such that the hydrostatic pressure in at least an uncased section of the borehole is above the pore pressure and below the fracture pressure in the surrounding subsurface formations or regions. If the hydrostatic pressure is lower than the pore pressure, a kick or blowout may occur. If the hydrostatic pressure is higher than the fracture pressure, a loss of the circulation of the mud in the borehole may occur. Fracture pressure typically increases rapidly with depth so that maintaining the hydrostatic pressure below the fracture pressure after drilling an initial section of the borehole is usually less of a problem. However, pore pressure generally follows a less predictable pattern. If the pore pressure ahead of the drill bit can be predicted, the mud weight needed to provide the desired hydrostatic pressure in the borehole can be determined prior to drilling an interval or distance ahead of current position of the drill bit, which facilitates in the avoidance of drilling hazards.